ios - 自动布局:无法同时满足约束

Question

我正在尝试使用自动布局和以下代码在容器 View 中堆叠多个 View :

UIView* prevView = commentBox; // Set the prev view to the container
for(Comment* comment in [[post info] comments]){
    UIView* commentView = [[UIView alloc] initWithFrame:CGRectZero];
    [commentView setTranslatesAutoresizingMaskIntoConstraints:NO];
    [commentBox addSubview:commentView];

    // Vertically align with container view
    [commentBox addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|[commentView]|" options:0 metrics:nil views:NSDictionaryOfVariableBindings(commentView)]];

    // Add a space of 8 between the previous view and the current view
    [commentBox addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:[prevView]-8-[commentView(==100)]" options:0 metrics:nil views:NSDictionaryOfVariableBindings(prevView, commentView)]];

    // Store the current view for the next round
    prevView = commentView;
}
// Finally, add a space between the last element and the container view
[commentBox addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:[prevView]-8-[commentBox]" options:0 metrics:nil views:NSDictionaryOfVariableBindings(prevView, commentBox)]];

commentBox 本身在 Storyboard中自动布局，这应该是安全的。

但是，当 commentBox 充满 subview 时，它会显示以下错误:

Unable to simultaneously satisfy constraints.
Probably at least one of the constraints in the following list is one you don't want.
Try this: (1) look at each constraint and try to figure out which you don't expect;
(2) find the code that added the unwanted constraint or constraints and fix it.
(Note: If you're seeing NSAutoresizingMaskLayoutConstraints that you don't understand, refer to the documentation for the UIView property translatesAutoresizingMaskIntoConstraints) 
(
    "<NSLayoutConstraint:0x170097ca0 H:|-(0)-[UIView:0x170199e60]   (Names: '|':UIView:0x17019a8f0 )>",
    "<NSLayoutConstraint:0x170097cf0 H:[UIView:0x170199e60]-(0)-|   (Names: '|':UIView:0x17019a8f0 )>",
    "<NSLayoutConstraint:0x174099280 UIView:0x17419c8a0.width == UIView:0x17019a8f0.width>",
    "<NSLayoutConstraint:0x17409a180 'UIView-Encapsulated-Layout-Width' H:[UIView:0x17419c8a0(320)]>",
    "<NSLayoutConstraint:0x170098ec0 H:[UIView:0x170199e60]-(8)-[UIView:0x1701997e0]>",
    "<NSLayoutConstraint:0x170098f10 H:[UIView:0x1701997e0(100)]>",
    "<NSLayoutConstraint:0x170099050 H:[UIView:0x1701997e0]-(8)-[UIView:0x170199a50]>",
    "<NSLayoutConstraint:0x1700990a0 H:[UIView:0x170199a50(100)]>",
    "<NSLayoutConstraint:0x170099190 H:[UIView:0x170199a50]-(8)-[UIView:0x17019b110]>",
    "<NSLayoutConstraint:0x1700991e0 H:[UIView:0x17019b110(100)]>",
    "<NSLayoutConstraint:0x174099dc0 H:[UIView:0x17019b110]-(8)-[UIView:0x170199e60]>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x174099dc0 H:[UIView:0x17019b110]-(8)-[UIView:0x170199e60]>

Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger.
The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKit/UIView.h> may also be helpful.

我不知道如何解决这个问题。

我正在使用带有 iOS SDK 8.1 的 xCode 6.1

提前致谢

Answer 1

我发现您的代码有两处错误。首先，您不能在第一个水平约束中使用 [prevView] 或在最后一个约束中使用 [commentBox] 来引用 super View 。您需要使用管道字符“|”来引用它。其次，你不能在整个 View 中一直设置硬约束(我指的是具有固定值的大小和空间)(除非这些数字都恰好加起来等于父 View 的宽度，即使那样你也不应该这样做它)。因此，您要么需要允许宽度或间距灵活，要么不要将最后一个约束限制在 commentView 的右侧。